Inductometer



June 30, 1925. 1,543,994

J. G. FERGUSON INnucToMETER Filed Dec. 1e, 1925 Patented June 30, 1925. l

. uNrrEnsTA'rEs PATENT oFFlcr-z.

Jon e. amusemor snoonxmunw Yoax, Assmann A'ro wrs'rm mac'rarc conm, mcoarona'rnn, or maw Yoan, n. La couronnes or anw Yoan.

Anuman ma member 1s, ma. ssi-iai iro. caisse.

To all wlurmit may concern:

Be it known that I, JOHN G. FanoUsoN, a subject of the King-of Great Britain residi at Brooklyn in the county of Kings l and tate of New York, have invented certain new and useful Im rovements in Inductometers, of which t e following is fa full, clear, concise, and exact description. This invention relates to inductometers,

l" and its object is to provide an inductometer having a small stray field.

The inductometers in common usefcomprise two sets of coils.' Inductometers of this nature are useful for many pur oses, l but they have a large stray lield an are therefore unsatisfactoryl for use as ,apparatus, suchv as precision bridges, in which other electrical instruments are used. Either the apparatus must be made so large as to be unwieldy, or considerable difficulty will-be found in the rigidness of certain of the instruments used therein.

In accordance with the general features of this invention, the number of sets of coils in the inductometer is increased by multiples of 2 and the size of the stray field correspondingly reduced. W'hile any desired number of sets of coils which is d1- visible by 2 may used, an inductometer 80 consisting of four sets ofiv coils arranged so as to approximate the form of a toroid has a suflicrently small stray field to be satisfactor in most cases.

he stationary coils in such an instru- 86 ment may be held in place, and the movement of the movable coils controlled, by any convenient mechanism. The drawings Ashow the stationa coils embedded in two -oppositel mounte pairs of coaxial hollow l0 truncatedy cones of insulating material and the movable coils embedded in twocones, each of which is mounted to rotate within one of said pairs of cones.

Fig. 1 is a side view of such an arrangement.

Fig. 2 is a view `of a rtion thereof when the movable coils are isplaced.

Fig. 3 shows diagrammatically the manner in which the coils are. electrically conl0 nected. v i

A pair of hollow, truncated, cones 4 and 5 are mounted one inside the other u n a mounting plate 6. These cones shoul prefadjusted. The centers of the cones in eac erably be rectangular,-that is, of such a nature that the apex of a bisected cone will be a right angle. A second pair of similar cones 14 and 15 are mounted oppositely to cones r4 and y5 upon a mountin plate 16 which isv held to, and distance from, plate Y 6 in any suitable manner. Within 60 each pair of cones are placed one of two hollow cones 7 and 17, which are mounted on a metallic shaft 8 rotatably set in plates Y 6 and 16.

Each of the cones is formed of insulating material, referably of a material such as vulcanizab e rubber or a phenolic condensation product, which ma be moulded from a fiat piece and hardene by heat or by heat and pressure. Two lcoils preferably having an oval shape are embedded in each of the pieces of insulating material, from which the cones are formed and are so positioned therein that each pair of stationary cones will contain two sets of concentric coils 10k and that each of the movable cones will contain two coils l1 which will be concentric with the coils 10 of their respective sets when the movable cones are suitably set will thus be along one of the sides of a square (or of a parallelogram if the cones are not rectangular one of whose axes corres onds to the axis of the cones.

he inductometer so formed is operated by the rotation of the shaft 8,' which is provided for this purpose with a knob 20 and a calibrated scale 21. Fig. 3 illustrates a method of electricall connecting the coils. The circuit exten from a terminal 22 in late 6, along a conductin strip 23 and 'ding contact 24, to the adtcent half of` shaft 8 which is se arated om the opposite half by an insulating joint 25. From here it passes through the four coils 11 in series, to the o posite half of shaft 8, sliding contact 26, through coils 10 in series, to a terminal 27 in plate 6. It will thus be seen" that the rotation of cones 7 and 17 containing coils 11 produces the same effect as the movemert of the movable coils in an inductometer of the ordina type.

e stray ield of the indnctometer illustrated will not extendappreciabl outside l the space between the plates 6 an 16, and

therefore will not affect the other electrical instruments used in connection with the inductometer.

Nliat is claimed is:

l. An inducir/)meter comprising coaxial supports, means to produce relative rotational movement between said supports, and an even number of sets of coils positioned on said supports and arranged so as to approximate the form of a toroid.

2. inductometer comprising coaxial truncated hollow cones, certain of said cones being movable and certain fixed, said movable cones being movable between said fixed cones, and sets of coils positioned in the surfaces or' said cones, said coils being ar ranged so as to approximate the form of a toroid.

3. An inductometer comprising coaxiai truncated cones, four pairs of fixedccils arranged in the surfaces of certain of said cones, the centers of said coils in each air falling along one of the sides of a paral elograln and iour movable coils arranged in the surfaces of others of said coaxial truncated cones, each of said movable coils being movable between the coils of two of said pairs.

4. In an inductometer, two o positely mounted stationary pairs of coaxia hollow truncated cones, a rotatable hollow cone within each of said pairs, two sets of concentric coils embedded in each pair of stationar cones, two coils so placed in each rotatable cone that they may be made concentric With the coils of said sets, and means to rotate the rotatable cones.

5. In an inductometer, two oppositely mounted stationary pairs of coaxia truncated, rectangular cones, a rotatable metallic shaft, an insulating 'ont dividing the shaft, a hollow truncated cone within each of said pairs of stationary cones and mounted u on one 'of the divisions of said rotatable sliaft, two sets of concentric coils embedded in each pair of stationary cones, livre coils so placed in each rotatable cone that they may be made concentric with the coils of said sets, means to rotate the shaft and an electrical circuit including all of said coils and the divisions of said shaft.

In witness whereof, I hereunto subscribe my name this l2 day of December A. D i923.

JOHN G. FERGUSON.

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